Composition for treating refractory materials for brazing

ABSTRACT

A coating composition that enables refractory materials such as ceramics to be joined to one another or to metallic components using brazing filler metals. The composition is applied on selected areas of the refractory material to define a target area for brazing. In one embodiment, the coating composition includes (i) a Group IVB transition metal component selected from the group consisting of a Group IVB transition metal, a hydride thereof, and mixtures of the Group IVB metals and/or hydrides thereof, (ii) a binder material, and (iii) a fluid carrier. In disclosed embodiments, the Group IVB transition metal component is titanium, and the binder material is a combination of a hydrocarbon resin and a styrene block copolymer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patent application Ser. No. 10/253,382 filed Sep. 24, 2002, which claims priority under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 60/324,857, filed Sep. 25, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a composition for treating refractory materials in such a manner as to facilitate bonding of the materials to one another.

2. Discussion of the Known Art

Non-metallic refractory materials such as ceramics are often used in applications that require such materials to be joined to other ceramics, or to metallic components. In the automotive industry, ceramics are used to form many parts that must be bonded firmly onto metallic support plates such as, e.g., high performance brake pads and linings made from aluminum nitride, aluminum oxide or zirconium oxide. In another example, technical ceramics are used in electrical and electronic applications such as power grid tubes, vacuum interrupters, semi-conductor packaging, multilayer substrates, ball grid arrays for electronic packaging, power dissipation packages, and sensor packages.

Typically, it is difficult to join ceramic materials to one another or to metallic components. Because existing brazing formulations do not adequately wet a refractory surface, metallization processes are usually performed on a ceramic prior to joining it to another ceramic or to a metal body. These processes involve multiple steps that form a bridge between a surface of the refractory material, and braze filler metals, solder metals, or conductive/protective metals that are used for printing electronic circuits on the material.

One example of a conventional metallization process involving a ceramic as the refractory body, involves four major steps, viz.;

-   -   1. Applying a molybdenum or molybdenum/manganese paste on a         desired area of the refractory body to be metallized (usually by         screening) and then air drying, or drying in an infrared oven         (e.g., at about 90 deg. C. to about 100 deg. C. for about 10 to         15 minutes);     -   2. Firing the product of step 1 in a controlled atmosphere         (e.g., a wet Hydrogen kiln at about 1200° C. to about 1500° C.;     -   3. Cleaning, etching, and nickel plating the product of step 2         using either an electroless or an electrolytic process, and         re-firing so as to sinter nickel into the molybdenum/manganese         coating; and     -   4. Placing a brazing filler metal in the form of a wire, foil,         ring, preform or powdered metal between the metallized section         of the refractory body and a metallized section of a body to be         joined, and then heating or firing the bodies to a temperature         above the liquidus of the brazing filler metal in an oxygen free         environment such as argon, dry hydrogen, ammonia gas, or a         vacuum.

For electronic circuit applications, there can be additional steps of cleaning and activating the nickel layer, and over plating with gold, silver, copper, or tin. Another composition and method used for metallizing is disclosed in U.S. Pat. No. 5,340,012, which is incorporated by reference herein. And see U.S. Pat. No. 3,063,144 (Nov. 13, 1962), and U.S. Pat. No. 5,056,702 (Oct. 15, 1991), also incorporated by reference.

SUMMARY OF THE INVENTION

The present invention relates to a coating composition for treating or metallizing surfaces of refractory materials, including non-metallic refractories such as ceramics, to facilitate bonding with like treated materials or with metallic components with the use of available brazing or soldering filler metals. The composition can be applied on selected areas of a refractory surface to define the target area for brazing. With suitable filler metals, a strong bond between two non-metallic refractory bodies, or between a non-metallic refractory body and a ferrous or non-ferrous material, can be attained.

The inventive coating composition is comprised of a Group IVB transition metal component selected from the group consisting of (i) a group IVB transition metal, a hydride thereof, mixtures of group IVB metals and/or hydrides thereof, (ii) a binder material, and (iii) a fluid carrier. For example, the group IVB transition metal component may be a group IVB transition metal selected from among titanium, zirconium, and hafnium, hydrides of the group IVB transition metals, and mixtures of these group members. In a preferred embodiment, the group IVB transition metal component is titanium, titanium hydride, or mixtures thereof.

Suitable binder materials may include, but are not limited to, hydrocarbon resins, modified hydrocarbon synthetic resins, gum rosins, tall oil rosins, wood rosins, modified rosin, acrylic polymer, natural and synthetic waxes, synthetic rubber like polyisobutylene, thermoplastic mixture of polybutylene and paraffin, water or solvent soluble cellulosic polymers, water soluble resins such as acrylic acid polymers, polyolefin and linear primary alcohols. Some gellant material like triblock, radial block and multiblock copolymers, optionally in conjunction with a diblock copolymer may also be employed. In one embodiment, the binder is a hydrocarbon resin. In a preferred embodiment, the binder includes a hydrogenated hydrocarbon resin and styrene block copolymer.

The fluid carrier employed in the inventive composition may include, but is not limited to, aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, and water. The fluid carrier of choice will depend on its compatibility with the chosen binder. Paraffinic hydrocarbons and hydro treated light petroleum distillate hydrocarbon solvents can be used herein.

In the preferred embodiment, the coating composition includes between approximately 10 and 90 weight percent of titanium or titanium hydride metal powder, and between approximately 90 and 10 weight percent binder and fluid carrier including hydrogenated hydrocarbon resins (available from Hercules), styrene block copolymer, and treated light petroleum distillate hydrocarbon fluid carrier (available from Penreco).

The present coating composition may have an ink-like to paste-like consistency, and can be applied though a screen. The consistency of the composition may be varied to achieve a desired shape and fineness of details. For example, the composition can be applied to a refractory surface by suitable coating techniques including, but not limited to, brushing, rolling and/or spraying. In selective applications, a suitable mask may be used to control the treated areas for rim sealing and joining, or to form electrical/electronic circuit traces.

Surface coating of ceramics with the inventive composition may allow more control of active metal concentration for interfacial compound development and, subsequently, joint strength. As a result, active metal depletion can be substantially reduced at ceramic surfaces, and deterioration of the physical properties of a braze filler due to excessive active metal concentrations (e.g., 8% or greater) will also be substantially reduced.

The present composition may have such a consistency as to permit screen-printing or stenciling, followed by a metallization/brazing process with suitable brazing filler metals so as to form circuit traces (e.g., conductive electronic or microwave circuits and elements) on refractory substrates. The composition is suited for use with oxide ceramics like alumina, zirconia, silica, and the like. In addition, most nitrides, carbides, diamonds (synthetic or natural), graphite or carbon, and sapphire (or similar gemstones) can be joined after being coated with the composition and without a need for the prior metallizing procedures.

After drying a refractory material on which the present composition has been applied, the treated surface can be metallized using a suitable brazing or solder filler metal and conventional brazing/soldering processes and equipment. For example, the surface can be heated in a substantially oxygen-free environment (e.g., argon, dry hydrogen, and/or vacuum) to a temperature above the liquidus of the brazing or solder filler metal.

For example, the following process can be used when the refractory body is a ceramic:

-   -   1. Coating (e.g., by brushing or screening) a surface on the         ceramic with the composition of the present invention. The         coating is then dried, either air dried at ambient conditions,         or at elevated temperatures between around 120° C. and 150° C.,         for about 10 to 20 minutes in order to accelerate drying; and     -   2. Applying a brazing filler metal in a preselected form (such         as a wire, foil, strip, shim, ring, perform, or powdered metal)         on the refractory body and brazing at suitable substantially         oxygen-free conditions (e.g., in vacuum, argon, or dry hydrogen         atmosphere) at a temperature appropriate for the selected         brazing filler metal.

The drying step (in 1., above) removes the fluid carrier and leaves a coating of the Group IVB transition metal component with the binder on the ceramic, thus facilitating later handling of the coated ceramic when joining the ceramic with another like-coated ceramic or a metallic part. After applying the brazing filler metal and undertaking the brazing step, the binder volatizes and is no longer present. The Group IVB transition metal component of the composition is believed to enhance the strength of the braze joint.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a coating composition than can be applied on a surface of a refractory material, including non-metallic materials, prior to brazing. The composition is comprised of (1) a Group IVB transition metal component selected from the group consisting of a Group IVB transition metal, a hydride of a Group IVB transition metal, and mixtures thereof, (2) a binder material, and (3) a fluid carrier. For example, the Group IVB transition metal component may be selected from among titanium, zirconium, and hafnium; hydrides of the group IVB transition metals, and mixtures thereof.

Suitable binder materials include, but are not limited to, hydrocarbon resins, modified hydrocarbon synthetic resins, gum rosins, tall oil rosins, wood rosins, modified rosin, acrylic polymer, natural and synthetic waxes, synthetic rubber like polyisobutylene, thermoplastic mixture of polybutylene and paraffin, water or solvent soluble cellulosic polymers, water soluble resins such as acrylic acid polymers, polyolefin and linear primary alcohols. Also included is a gellant material like triblock, radial block and multiblock copolymers, optionally in conjunction with a diblock copolymer. In one embodiment, the binder includes a hydrocarbon resin. In a preferred embodiment, the binder is a hydrogenated hydrocarbon resin and styrene block copolymer.

A fluid carrier is also part of the composition. A non-exhaustive list of fluid carriers includes aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, and water. The fluid carrier of choice will depend on its compatibility with the chosen binder. The composition may use either a paraffinic hydrocarbon fluid carrier or a hydro treated light petroleum distillate hydrocarbon fluid carrier.

In one embodiment, the composition includes between about 10 and 90 weight percent of the Group IVB transition metal component in a powder form, and between about 90 and 10 weight percent binder and fluid carrier.

In a preferred embodiment, the composition includes between about 10 and 90 weight percent of titanium or titanium hydride metal powder, and between about 90 and 10 percent binder and fluid carrier. The composition may have a consistency suited for brushing, rolling, spraying or screening, and stenciling on the refractory surface.

As used herein, the term “binder” refers to a material or materials that, when present in the composition of the invention, (1) facilitates the binding of the Group IVB transition metal component to a refractory body, ferrous body, or non-ferrous body, or (2) helps maintain the Group IVB transition metal component in a stable suspension within the fluid carrier, or (3) performs both of these functions.

As used herein, the term “fluid carrier” refers to a fluid material that serves as a carrying agent for the Group IVB transition metal component and the binder. The fluid carrier is volatizable at temperatures lower than the temperatures at which brazing or soldering will be effected. In some instances, the carrier may be a solvent for the Group IVB transition metal component and/or the binder.

Binders include, but are not limited to, hydrogenated hydrocarbon resins (available from Hercules under the trade name Regal Rez), and di-and tri-block copolymers based on thermoplastic rubbers, such as styrene block copolymers (available from Penreco). Suitable fluid carriers include, but are not limited to, isoparaffinic hydrocarbons available under the trade name Isopar from Exxon, and hydrogenated light distillates available under the trade name Conosol from Penreco.

A combination of styrene block copolymer binder and fluid carrier, for example, “Versagel” and “Synergel” both available from Penreco, are suited also for use in the composition of the present invention.

After the composition is applied on a refractory surface, the fluid carrier is removed from the composition by either air drying or heating so that a coating of the Group IVB transition metal component remains with the binder on the surface. Subsequently, after the brazing filler metal is set in place and brazing is undertaken, the binder volatizes at temperatures below the brazing temperature, thus leaving little or no residue and not interfering with or contaminating the braze joint.

EXAMPLES OF COATING COMPOSITIONS

The following chart shows examples of coating compositions according to the invention. It will be understood that equivalent suitable materials may also form part of the present invention. Ingredient Trade Name Weight % 1. Active Metal Titanium powder, 10 to 90% Zirconium powder, Hafnium or any Group IVB elements, and hydrides of these elements. Mixtures of above are also suitable. 2. Binder Di or tri block copolymers Available from the  1-50% based on thermo-plastic Penreco Division of rubbers such as styrene Pennzoil block copolymers. Modified hydrocarbon Regalrez 1126 Resin  1-10% synthetic resins 3. Fluid carrier Isoparaffinic Isopar G 15-50% Hydrocarbon Hydrogenated light Conosol 145 15-50% Distillate

Active metals from Group IVB, including combinations of elements such as titanium and zirconium, may be used to form a eutectic having a lower liquidus temperature or to meet other special requirements. The particle size of the Group IVB transition metal powder should be sufficient to pass through a −325 mesh screen, although other mesh sizes of between −80 and −400, or a particle size of not more than about 250 microns, may also be effective.

The type and/or amount of fluid carrier in the inventive composition may be selected so as to adjust the viscosity of the composition. As shown in the above chart, either or a combination of two or more types of fluid carriers may be used in the composition. For example, an isoparaffinic hydrocarbon may be used alone or combined with another fluid carrier such as hydrogenated light distillate. A plurality of the fluid carriers, including those disclosed in the chart, may be combined in any appropriate ratio so as to result in a desired viscosity and/or sufficient carrier properties for the composition.

In one embodiment, titanium or titanium hydride metal powder having a mesh size of about −325 is mixed with the binder. The mixture comprises about 35 weight percent titanium, 65 weight percent binder having hydrogenated hydrocarbon resins (Hercules) and/or styrene block copolymer, and treated light petroleum distillate hydrocarbon fluid carrier (Penreco ). This mixture has a proper consistency for brushing, rolling or spraying the refractory surface.

The mixture is then coated on a refractory body in an amount sufficient to apply the Group IVB transition metal in a percent range that is typically between about 2 and 8 weight percent of the combined weight of the braze metal and the Group IVB transition metal, with about 4 to 6 weight percent of the Group IVB transition metal being well suited for this application.

In another example, titanium or titanium hydride metal powder having a mesh size of about −325 or smaller (44 microns or smaller) is mixed with the binder. The mixture comprises about 65% weight titanium, about 35% weight binder having hydrogenated hydrocarbon resins (Hercules) and styrene block copolymer, and treated petroleum distillate hydrocarbon fluid carrier (Penreco). This mixture has a consistency suitable for screening or stenciling onto a refractory body.

The present invention is used in conjunction with one or more brazing filler metals or metal alloys to join a refractory material to a metallic component or surface. Suitable brazing filler metals include, but are not limited to, conventional braze alloy such as a silver-copper eutectic composition (e.g., 72% silver and 28% copper), silver-copper alloys including from about 50 to 85 weight percent silver, and from about 15 to 50 weight percent copper; alloys of silver-copper-nickel, or silver-copper-indium (e.g., silver-copper-nickel alloys comprising from about 50 to 85 weight percent silver, from 15 to 50 weight percent copper and from about 0.2 to 2.5 weight percent nickel, and the silver-copper-indium alloys comprising from about 50 to 70 weight percent silver, from about 15 to 35 weight percent copper, and from about 10 to 20 weight percent indium), or the eutectic alloys of these metals.

A wide range of other available brazing filler alloys can be used for joining similar or dissimilar base materials or components. For example, alloys containing copper, nickel, tin, silver, gold, molybdenum, cobalt, or palladium, along with additives such as boron or the like. Other examples of brazing filler metals include nickel base materials, gold-nickel alloys, and semi-amorphous materials. As mentioned, the brazing filler metal used with the present invention can be of any suitable shape and form, for example, a wire, foil, strip, shim, ring, preform, or powdered metal.

The inventive composition is also suited for use with oxide ceramics like alumina, zirconia, silica, etc. In addition, most nitrides, carbides, diamonds (synthetic or natural), graphite or carbon, and sapphire (or similar gemstones) can be joined without the need for prior metallizing procedures.

Example One

A composition having an ink-like consistency has the following formulation. All percentages are by weight: Titanium powder:   35% Binder Regal Rez:  6.5% Di- or tri-block copolymers based on 16.25% thermoplastic rubbers such as styrene block copolymers in a hydrogenated light hydrocarbon distillate: Fluid carrier (Isopar): 42.25%

Example Two

A composition with a paste-like consistency, suited for stenciling and screening, has the following formulation. All percentages are by weight: Titanium:   55% Isopar fluid carrier:   5% Binder Regal Rez: 19.4% Di- or tri-block copolymers based on thermoplastic 20.6% rubbers such as styrene block copolymers in a hydrogenated light hydrocarbon distillate:

The “Regal Rez” is dissolved either directly into the fluid carrier, or into the di-or tri-block copolymers based on thermoplastic rubbers (such as styrene block copolymers) when supplied in a hydrogenated light hydrocarbon distillate carrier, using any standard mixing process. Heat can be used to expedite the process but is not necessary. The titanium is added to form a smooth homogeneous mixture.

While the foregoing represents preferred embodiments of the invention, it will be understood by those skilled in the art that various modifications and changes may be made without departing from the spirit and scope of the invention, and that the invention includes all such modifications and changes as come within the scope of the following appended claims. 

1. A coating composition for preparing a surface of a refractory material for joining with a like-coated refractory material or a metallic component, comprising: a Group IVB transition metal component selected from the group consisting of a Group IVB transition metal, a Group IVB transition metal hydride, and mixtures thereof; a binder including a hydrocarbon resin and styrene block copolymer; and a fluid carrier.
 2. The coating composition of claim 1, wherein the binder comprises a hydrogenated hydrocarbon resin.
 3. The coating composition of claim 1, wherein the Group IVB transition metal component comprises between about 10 and 90 weight percent titanium or titanium hydride metal powder, and the binder comprises between about 90 and 10 weight percent of a hydrogenated hydrocarbon resin and styrene block copolymer.
 4. The coating composition of claim 1, wherein the fluid carrier is selected from the group consisting of aliphatic hydrocarbon solvents, aromatic hydrocarbon solvents, alcohols, ketones, esters, glycol, glycol ether, glycerin, water, paraffinic hydrocarbon solvents, hydro treated light petroleum distillate hydrocarbon solvents, and mixtures thereof.
 5. The coating composition of claim 1, wherein the Group IVB transition metal component is in the form of a powder with a mesh size of between about −80 and −400.
 6. The coating composition of claim 1, wherein the Group IVB transition metal component is in the form of a powder with a mesh size of about −325.
 7. First and second non-metallic refractory bodies each of which has a surface that is coated with the composition of claim 1, and the bodies are joined to one another by placing a brazing filler metal alloy between the coated surfaces of the bodies and heating the bodies to a liquidus temperature of the brazing filler metal alloy.
 8. The joined refractory bodies of claim 7, wherein the transition metal component of the composition is present in an amount of between about 2 and 8 weight percent of a combined weight of the transition metal component and the brazing filler metal alloy.
 9. A non-metallic refractory body, and a ferrous or non-ferrous metal body, wherein at least the non-metallic refractory body has a surface that is coated with the composition of claim 1, and the bodies are joined to one another by placing a brazing filler metal alloy on the coated surface of the non-metallic refractory body and heating the bodies to a liquidus temperature of the brazing filler metal alloy.
 10. The joined bodies of claim 9, wherein the transition metal component of the composition is present in an amount of between about 2 and 8 weight percent of a combined weight of the transition metal component and the brazing filler metal alloy.
 11. A coating composition according to claim 1, wherein the transition metal component comprises titanium, zirconium, hafnium, or mixtures thereof.
 12. (canceled)
 13. A coating composition according to claim 1, wherein the composition is comprised of about 35 weight percent of the transition metal component, and about 65 weight percent of the binder and the fluid carrier.
 14. A coating composition according to claim 1, wherein the composition is comprised of about 65 weight percent of the transition metal component, and about 35 weight percent of the binder and the fluid carrier.
 15. An article of manufacture, comprising: a metallic component having a first surface; and a ceramic component joined to the metallic component, wherein the ceramic component has a second surface and is joined to the ceramic component by: coating the second surface of the ceramic component with the coating composition of claim 1; drying the coated second surface; placing a brazing filler metal alloy in a given form on said coated second surface; and brazing the first surface of the metallic component to the second surface of the ceramic component.
 16. An article of manufacture according to claim 15, wherein the transition metal component of the composition is present in an amount of between about 2 and 8 weight percent of a combined weight of the transition metal component and the brazing filler metal alloy. 